1st ICAI 2020

International Conference on Automotive Industry 2020

Mladá Boleslav, Czech Republic

3.2.2 Thermal direct joining with laser and induction Similar to adhesive bonding tests, the metallic joining partner were pre-treated as described in chapter 3.1. PLA was only cleaned with isopropanol. Then the partner were pressed together and heated up and cooled down under pressure, as shown in chapter 2.3 for 1.5 s (induction), respectively 5 s (laser). After cooling, the second joining step was done to generate the above mentioned double-lap joint. After mechanical testing the fractured surfaces were characterised. While no connection could be achieved with the reference pre-treatment (cleaning with isopropanol), a surface roughening by sand blasting realised strengths comparable to adhesive bonding. Using laser macro structuring, shear strength of 17 – 23 N/mm² were reached. As can be seen in Figure 4 left a form-fit can be realised between PLA and metal. This mechanism results mostly in cohesive failure within the PLA and partly mixed fracture (Figure 6 right). Figure 6: Tensile shear strength of directly joined PLA + aluminium joints for different pre-treatment processes on the metal side; pre-treatment PLA: isopropanol cleaning (left); fractured surfaces: induction heating (top right), laser heating (bottom right)

Source: own elaboration 3.3 Adhesive bonding of PLA, PET, PP

As described above, joining tests of different plastic types were realised too. In order to carry the tests out as comparable as possible, PET and PP with the same thickness and the same surface pre-treatments were adhesively bonded with DP400. The results of the mechanical testing are shown in Figure 7. A large difference between all three material types is apparent. While all thermoplastics possess a low energetic surface, the PP interacts with the adhesive in an excellent way. Shear strengths of up to 15 N/mm² in combination with partly cohesive failure within the PP were observed. The white colour in Figure 7 right represents the damage within the plastic.

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